Growth, water relations, and nutritive value of pasture species mixtures under moisture stress

Pasture productivity under harsh environments can be increased by planting more drought-resistant species or by increasing species diversity. This research was conducted under two large (10.2 x 26.8 m) rainout shelters combined with a drip irrigation system to provide deficit, normal, and excessive moisture conditions. A two-species mixture containing the relatively drought-tolerant species, orchardgrass (Dactylis glomerata L.) and red clover (Trifolium pretense L.) and two five-species mixtures were compared with a mixture containing the drought-sensitive species, white clover (Trifolium repens L.) and Kentucky bluegrass (Poa pratensis L.), which are the predominant species in northeastern USA pastures. Plots were clipped from mid-May to early October in 2000 and 2001 on a schedule that mimicked management-intensive grazing practices. The five-species mixture containing chicory (Cichorium intybus L.), orchardgrass, Kentucky bluegrass, perennial ryegrass (Lolium perenne L.), and white clover had the greatest dry matter yield at all moisture levels. Yield in that mixture increased 89% in the dry, 61% in the normal, and 43% (by weight) in the wet treatments compared with the white clover/ Kentucky bluegrass mixture. Increased yield was primarily due to the robust growth of chicory which dominated the mixture, accounting for 71% of harvested biomass by the fall of 2001. In addition, white clover growing in the mixture with chicory had improved leaf water relations and greater relative growth rates than white clover growing in the two-species mixture. Including the functional attribute of a deep-rooted forb appeared to be more important than species richness, per se, in improving forage yield.